Electronic paper

A prototype E-Ink display

Electronic paper, also sometimes called e-paper, Electronic ink or e-ink, is a display technology using organic electronics designed to mimic the appearance of regular ink on paper. Unlike a conventional flat panel display, which uses a backlight to illuminate its pixels, electronic paper reflects light like ordinary paper and is capable of holding text and images indefinitely without drawing electricity or using processor power, while allowing the paper to be changed. One important feature needed is that the pixels be bistable so that the state of each pixel can be maintained without a constant supply of power.

Electronic paper was developed in order to overcome some of the limitations of computer monitors. For example, the backlighting of monitors is hard on the human eye, whereas electronic paper reflects light just like normal paper. It is easier to read at an angle than flat screen monitors. It is lightweight, durable, and highly flexible compared to other display technologies, though it is not as flexible as paper.

Predicted future applications include e-paper books capable of storing digital versions of many books, with only one book displayed on the pages at any one time. Electronic posters and similar advertisements in shops and stores have already been demonstrated.

Technology

Electronic paper was first developed in the 1970s by Nick Sheridon at Xerox's Palo Alto Research Center. The first electronic paper, called Gyricon, consisted of tiny, statically charged balls that were black on one side and white on the other. The "text" of the paper was altered by the presence of an electric field, which turned the balls up or down.

In the 1990s another type of electronic paper was invented by Joseph Jacobson, who later co-founded the corporation E Ink which formed a partnership with Philips Components two years later to develop and market the technology. This used tiny microcapsules filled with electrically charged white particles suspended in a colored oil. In early versions, the underlying circuitry controls whether the white particles were at the top of the capsule (so it looked white to the viewer) or at the bottom of the capsule (so the viewer saw the color of the oil). This was essentially a reintroduction of the well-known electrophoretic display technology, but the use of microcapsules allowed the display to be used on flexible plastic sheets instead of glass.

One early version^[1] of electronic paper comprises of a sheet of very small transparent capsules, each about 40 micrometres across. Each capsule contains an oily solution containing black dye (the electronic ink), with numerous white titanium dioxide particles suspended within. The particles are slightly negatively charged, and each one is naturally white.

The microcapsules are held in a layer of liquid polymer, sandwiched between two arrays of electrodes, the upper of which is made from indium tin oxide, a transparent conducting material. The two arrays are aligned so that the sheet is divided into pixels, which each pixel corresponding to a pair of electrodes situated either side of the sheet. The sheet is laminated with transparent plastic for protection, resulting in an overall thickness of 80 micrometres, or twice that of ordinary paper.

File:E-ink.png

The network of electrodes is connected to display circuitry, which turns the electronic ink 'on' and 'off' at specific pixels by applying a voltage to specific pairs of electrodes. Applying a negative charge to the surface electrode repels the particles to the bottom of local capsules, forcing the black dye to the surface and giving the pixel a black appearance. Reversing the voltage has the opposite effect - the particles are forced to the surface, giving the pixel a white appearance.

A more recent incarnation^[2] of this concept requires only one layer of electrodes beneath the microcapsules.

Another early version^[1] uses polyethylene spheres between 20 and 100 micrometres across instead of capsules. Each sphere consists of negatively charged black plastic on one side and positively charged white plastic on the other. The spheres are embedded in a transparent silicone sheet, with each sphere suspended in a bubble of oil so that they can rotate freely. The polarity of the voltage applied to each pair of electrodes then determines whether the white or black side is face-up, thus giving the pixel a white or black appearance.

Polychrome e-paper

Simple colour e-paper^[3] consists of a thin coloured optical filter added to the monochrome technology described above. The array of pixels is divided into triads, typically consisting of the standard red, green and blue, in the same way as CRT monitors. The display is then controlled like any other electronic colour display.

Applications

There are many approaches to electronic paper, with many companies developing technology in this area. Other technologies being applied to electronic paper include modifications of liquid crystal displays, electrochromic displays, and the electronic equivalent of an Etch-A-Sketch at Kyushu University. One form or another of electronic paper is being developed by Gyricon (which was spun out of Xerox), Philips Electronics, Kent Displays (cholesteric displays), NTERA(electrochromic NanoChromics(tm) displays), SiPix Imaging (electrophoretic), and many others.

In April, 2004, Sony announced the first commercially available electronic paper device, the LIBRIe, sold only in Japan. On January 6, 2006, Sony announced the Sony Reader, a successor to the LIBRIé for the US market.

On July 14th and 15th 2005 Fujitsu showcased their jointly developed electronic paper at the Tokyo International Forum. It boasts low power consumption in that it does not require electricity except during screen image changes, making electronic paper especially suited for advertisements or information bulletins in public places for which paper is currently used.

E Ink announced in October 2005 that it would begin shipping developer kits of 6 inch, 800x600 resolution electronic paper on November 1st, 2005.

In December 2005 Xerox announced it was closing the Gyricon operation as of December 31, 2005.

Another electronic paper device to be introduced in April of 2006 is the iLiad produced by iRex Technologies BV (a spinoff from Royal Philips Electronics). It would be able to render content without DRM based restrictions, and supports PDF, XHTML, TXT and MP3 formats. It also has standard connectivity features for transferring content, namely USB stick/cable, Compact Flash, SD Memory Card, WiFi, and Ethernet access.

In February 2006, the Flemish daily De Tijd of Antwerp announced plans to distribute an electronic-ink version of the paper to selected subscribers. This was the first such application of electronic ink to newspaper publishing.

Given their thinness and flexibility, electronic paper displays are now being embedded in smart cards. Flexible display cards enable financial payment cardholders to generate a one-time password to reduce online banking and transaction fraud. Compared with existing key fob tokens, display cards offer a flat and thin alternative to existing key fob tokens for data security. The world’s first ISO compliant smart card with an embedded display was developed by Smartdisplayer using SiPix Imaging’s electronic paper.

Motorola's new candybar-format mobile phone, called the MOTOFONE, is also expected to use an electronic paper screen, probably similar to the Sony Reader.

Electronic paper should not be confused with digital paper.

References

^ ^a ^b New Scientist. Paper goes electric (1999)
^ New Scientist. Roll the presses (2001)
^ New Scientist. Read all about it

Journals

Advanced Materials, vol 14, p 1460

External links

[newscientist_1-1] New Scientist. Paper goes electric (1999)

[2] New Scientist. Roll the presses (2001)

[3] New Scientist. Read all about it

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